Re: How expensive is getting the RTTI ?

From:
"Thomas J. Gritzan" <Phygon_ANTISPAM@gmx.de>
Newsgroups:
comp.lang.c++
Date:
Sun, 02 Jul 2006 01:30:28 +0200
Message-ID:
<e870if$b0d$1@newsreader2.netcologne.de>
benben schrieb:

Thanks Ben. As of now, instead of dynamic_cast, we have just put
virtual int getSize() { return sizeof(*this);}
in all the classes of the hierarchy (some 4-5). And in myFunc, we did
ptr + i*ptr->getSize()
instead of using ptr[i]

I know this is not very elegant and especially if someone adds a new
class, he _has_ to override this method. But this is some old legacy
code and I dont want to change a lot here. And am pretty sure, there
wont be new classes added.
Thanks,
Vikram


Wow, I didn't know you have an array to BaseC instead of an array to
BaseC*. How did you convert DerivedC[], say, to BaseC[]?

There is a design problem here: why do you have an array to BaseC (not
BaseC*) instead of an array to DerivedC?

As with the legacy code, if you 1) are so confident that the BaseC[]
array is indeed a DerivedC array, and 2)want to bypass the runtime type
checking, then why don't you just use static_cast?

void myFunc( baseC ptr[], int length) {
   DerivedC* ptr2 = static_cast<DerivedC*>(&ptr[0]);

   for (int i=0; i<length; i++)
       ptr2[i].someField = somevalue;
}


Because he wants to use this function polymorphically with baseC[] and
DericedC[]?

Thomas

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